Active acoustic attenuation involves injecting a secondary sound to destructively interfere with and cancel a primary sound. Describing the primary sound by the unwanted pressure fluctuation p.sub.P (x, t)) then the secondary pressure fluctuation p.sub.s (x, t) has to be equal in magnitude and in opposite phase (180.degree.), to obtain a total pressure fluctuation p(x,t)=p.sub.s (x, t)+p.sub.P (x, t)=0. The generation of the required secondary sound requires an accurate model of the transformation that the primary sound undergoes as it propagates along the path to the source of the secondary sound.